.TH astrometry 1 "November 2009" Munipack
.SH NAME
astrometry \- estimate astrometrical solution
.SH SYNOPSIS
astrometry [options]
.SH DESCRIPTION
Astrometry computes parameters of certain analytical transformation 
between spherical coordinates (for example Right Ascension and Declination) 
and a rectangular projection of the coordinates (for example pixels
on array detector).
.PP
The transformation includes a projection (gnomonical), a scale and
a rotation in a projected coordinates. The projection is computed
by a standard formulae. The scale is computed as robust mean of
ratios of euclidean distances between the projected coordinates and pixels.
The rotation is computed by a robust least square method. A complete
solution is iterated to find a priory unknown centre of the projection.
.PP
The astrometry is computed from an input data: catalogue coordinates
and measured centroids of objects (stars). To pass the input parameters
to this utility, see section FILES.
.PP
The astrometrical solution is printed in a text format which is 
directly usable in a FITS header.
.SH FILES
The format of input is a text file with two types of records:
1. parameters starting with a keyword, 2. coordinates. Keywords
are equivalent to FITS WCS. The comments are introduced by '#'.
.PP 
Mandatory parameters are:
.PP
CRPIX1, CRPIX2 <number> \- centre of projection in rectangular coordinates 
(pixels) on chip
.PP
NDAT <number> \- number of data points
.PP
Records with data points must follow NDAT and their counts must corresponds.
A minimal number of data points is two.
The records consists from two pairs of real numbers. The first pair
represents spherical coordinates in degrees. The second pair are rectangular 
coordinates.
.PP
Optional parameter:
.PP
DEBUG \- print additional information (if positive), defaultly set to zero
.PP.
Minimal example for image 640x480 pixels:
.PP
.PD 0
.LP
WCSAXES 2
.LP
RADESYS 'ICRS'
.LP
CRPIX1 320
.LP
CRPIX2 240
.LP
NDAT 13
.LP
        269.5530648     +04.6653512     83.38   193.62
.LP
        269.5380418     +04.6576759     122.22  171.77
.LP
        269.4990630     +04.6465214     223.88  138.35
.LP
....
.PD
.PP
Parameters RADESYS,EQUINOX and WCSAXES are not used by this utility, but
ones should be presented in any correct astrometrical description of the
transformation.
.SH SEE ALSO
http://munipack.physics.muni.cz/
.SH AUTHORS
F.Hroch <hroch@physics.muni.cz>
